Ultra Wideband Communication System, Transmission Device Reception Device, and Replay Device Used for the Same

ABSTRACT

The ultra wideband communication system comprises: a pulse generation section for generating a pulse signal based on a data signal; a first optical phase modulation section for performing optical phase modulation in accordance with the pulse signal, and outputting a resultant signal as an optical pulse signal; an optical transmission path for propagating the optical pulse signal; a template generation section for outputting a template signal; a second optical phase modulation section for performing optical phase modulation on the optical pulse signal in accordance with the template signal, and outputting a resultant signal as an optical phase demodulation signal; an optical phase intensity conversion section for converting information about an optical phase of the optical phase demodulation signal into information about an optical intensity thereof, and outputting a resultant signal as an optical correlation signal; an optical-electrical conversion section for performing optical-electrical conversion on the optical correlation signal, and outputting a resultant signal as a correlation signal; and a signal identification section for identifying the correlation signal outputted from the optical-electrical conversion section, thereby detecting the data signal.

TECHNICAL FIELD

The present invention relates to an ultra wideband communication systemcalled UWB (Ultra Wide Band) for transmitting a light, which has beenmodulated by using a short-pulse signal which is an ultra widebandsignal, and demodulating the light. The present invention particularlyrelates to an ultra wideband communication system in which correlationprocessing for demodulating the light is performed in a distinctivemanner.

BACKGROUND ART

Conventionally, there has been an ultra wideband communication system inwhich correlation processing is performed electrically (refer to, e.g.,a patent document 1). Also, there has been a proposed system forconverting an electrical pulse signal into an optical signal,transmitting the optical signal on an optical transmission path, anddemodulating the optical signal into an electrical pulse signal (referto, e.g., International Publication WO 2004/082175). FIG. 9A is a blockdiagram showing an ultra wideband communication system as a result of:extracting, from a conventional ultra wideband communication systemdisclosed in the patent document 1, component elements relating to thepresent invention; and adding, to the extracted component elements,component elements required for performing optical transmission whichare disclosed in International Publication WO 2004/082175.

A configuration of such a conventional ultra wideband communicationsystem is described below. In FIG. 9A, the conventional ultra widebandcommunication system performs a transmission of a data signal from anoptical modulation section 90 to an optical demodulation section 95 viaan optical transmission path 94. The optical modulation section 90comprises a signal generation section 91, a pulse generation section 92and an electrical-optical conversion section 93. The opticaldemodulation section 95 comprises an optical-electrical conversionsection 96, a correlation section 97, a template generation section 98and a signal identification section 99.

FIG. 9B shows waveforms of pulse signals outputted from the pulsegeneration section 92. FIG. 9B shows, with a dashed line, a waveformcorresponding to data “0”, and shows, with a solid line, a waveformcorresponding to data “1”. FIG. 9C shows waveforms of optical pulsesignals outputted from the electrical-optical conversion section 93.FIG. 9C also shows, with a dashed line, a waveform corresponding to data“0”, and shows, with a solid line, a waveform corresponding to data “1”.

Hereinafter, operations of a conventional ultra wideband communicationdevice will be described with reference to FIGS. 9A to 9C. In theoptical modulation section 90, the signal generation section 91 outputsa data signal to be transmitted. The pulse generation section 92generates a pulse signal (refer to FIG. 9B) based on the data signaloutputted from the signal generation section 91, and outputs the pulsesignal. The electrical-optical conversion section 93 performs opticalintensity modulation on the pulse signal outputted from the pulsegeneration section 92, and outputs a resultant signal as an opticalpulse signal (refer to FIG. 9C).

The optical transmission path 94 propagates the optical pulse signaloutputted from the electrical-optical conversion section 93.

In the optical demodulation section 95, the optical-electricalconversion section 96 converts the optical pulse signal havingpropagated through the optical transmission path 94 (refer to FIG. 9C)into a pulse signal (refer to FIG. 9B), and outputs the pulse signal.The template generation section 98 generates a pulse having acorrelation with the pulse signal, and outputs the pulse as a templatesignal. The correlation section 97, which is structured by, e.g., anelectrical mixer, multiplies amplitude information about the pulsesignal outputted from the optical-electrical conversion section 96 byamplitude information about the template signal outputted from thetemplate generation section 98, thereby obtaining a correlation betweenthe pulse signal and the template signal, and then outputs a resultantsignal as a correlation signal. Hereinafter, processing by thecorrelation section 97 for obtaining the correlation between the pulsesignal and the template signal will be referred to as correlationprocessing. The signal identification section 99 integrates thecorrelation signal outputted from the correlation section 97, therebyidentifying the data signal transmitted from the optical modulationsection 90.

An operation related to each signal (data signal, pulse signal, opticalpulse signal, template signal and correlation signal) which is performedfor correlation processing will be described in detail. As shown by thewaveforms of FIG. 9B, when a data signal is “1”, the pulse generationsection 92 generates a pulse signal having a polarity in which anamplitude of the pulse signal changes from minus to plus, whereas when adata signal is “0”, the pulse generation section 92 generates a pulsesignal having an opposite polarity to that of the pulse signal generatedwhen the data signal is “1”. The electrical-optical conversion section93 converts the amplitude of the pulse signal into optical intensityinformation, and generates an optical pulse signal having a samepolarity as that of the pulse signal. The template generation section 98generates a pulse, which has a fixed polarity regardless of a content ofthe data signal, i.e., a predetermined template signal. Consequently, avalue, which is indicated by a correlation signal obtained frommultiplying the amplitude information about the pulse signal by theamplitude information about the template signal, is different between acase where the pulse signal and template signal have a same polarity anda case where the pulse signal and template signal respectively havedifferent polarities. This allows the signal identification section 99to recognize whether the data signal is “1” or “0” by integrating thecorrelation signal over one cycle of one optical pulse signal. Notethat, the optical modulation section 90 and the optical demodulationsection 95 are synchronized in a conventional manner. In accordance withsuch synchronization, the correlation section 97 obtains a correlationbetween the template signal and the pulse signal.

-   [Patent Document 1] Japanese National Phase PCT Laid-Open    Publication No. 11-504480 (page 47, FIG. 17)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the above-described conventional system configuration, the opticaldemodulation section 95 performs correlation processing by using thecorrelation section 97 such as an electrical mixer. Generally speaking,it is difficult to obtain a wideband frequency characteristic by anelectrical mixer. Therefore, in the conventional system configuration asshown in FIG. 9A, there is a problem that a quality of correlationprocessing is prone to deteriorate.

In addition, when the above-described optical transmission of pulsesignals is used for wavelength division multiplexed transmission, eachof the number of correlation sections and the number of templategeneration sections is required to correspond to the number ofwavelengths. This results in a problem that a device for the systemincreases in size.

Therefore, an object of the present invention is to provide an ultrawideband communication system capable of preventing a deterioration of aquality of correlation processing. Another object of the presentinvention is to provide an ultra wideband communication system which is:capable of preventing a deterioration of a quality of correlationprocessing; capable of preventing a device for the system fromincreasing in size; and applicable for wavelength division multiplexing.

Solution to the Problems

In order to solve the above-mentioned problems, the present inventionhas the following features. A first aspect of the present invention isan ultra wideband communication system for converting a pulse signalinto an optical pulse signal, transmitting the optical pulse signal, anddemodulating the transmitted optical pulse signal, the system comprisingat least one pulse generation section for generating the pulse signalbased on a data signal; at least one first optical phase modulationsection for performing optical phase modulation in accordance with thepulse signal generated by the pulse generation section, and outputting aresultant signal as the optical pulse signal; an optical transmissionpath for propagating the optical pulse signal outputted from the firstoptical phase modulation section; a template generation section forgenerating a pulse which has a correlation with the pulse signal andwhich has a predetermined waveform, and outputting the pulse as atemplate signal; a second optical phase modulation section for, inaccordance with the template signal outputted from the templategeneration section, performing optical phase modulation on the opticalpulse signal propagated through the optical transmission path, andoutputting a resultant signal as an optical phase demodulation signal;an optical phase intensity conversion section for converting informationabout an optical phase of the optical phase demodulation signaloutputted from the second optical phase modulation section intoinformation about an optical intensity thereof, and outputting aresultant signal as an optical correlation signal; at least oneoptical-electrical conversion section for performing optical-electricalconversion on the optical correlation signal outputted from the opticalphase intensity conversion section, and outputting a resultant signal asa correlation signal; and at least one signal identification section fordetecting the data signal by identifying the correlation signaloutputted from the optical-electrical conversion section.

According to the first aspect of the present invention, a first opticalphase modulation is performed at the transmitting end in accordance withthe pulse signal, and as a result, the optical pulse signal isoutputted. The optical pulse signal is propagated, and a second opticalphase modulation is performed at the demodulating end in accordance withthe template signal. By the second optical phase modulation, a phase ofthe optical pulse signal is added to a phase of the template signal, andas a result, the optical phase demodulation signal having correlationswith the optical pulse signal and the template signal is outputted. Theoptical phase intensity conversion section converts information about anoptical phase of the optical phase demodulation signal into informationabout an optical intensity thereof, and as a result, the optical phasedemodulation signal is converted into the optical correlation signal. Byconverting the optical correlation signal into an electrical signal, acorrelation between the pulse signal based on the original data signaland the template signal is obtained. Accordingly, the original datasignal can be detected by identifying the correlation signal. Thus, thepresent invention provides an ultra wideband communication system, whichperforms correlation processing by using an optical device and which iscapable of preventing a deterioration of a quality of correlationprocessing.

In a second aspect of the present invention, more than two: pulsegeneration sections; first optical phase modulation sections;optical-electrical conversion sections; and signal identificationsections are provided. The ultra wideband communication system furthercomprises: a wavelength division multiplexing section for performingwavelength division multiplexing of optical pulse signals respectivelyoutputted from the first optical phase modulation sections, and thenpropagating the optical pulse signals through the optical transmissionpath; and a wavelength demultiplexing section provided on an output sideof the optical phase intensity conversion section. The second opticalphase modulation section performs, in accordance with the templatesignal outputted from the template generation section, optical phasemodulation on a plurality of optical pulse signals multiplexed by thewavelength division multiplexing section, and outputs resultant signalsas optical phase demodulation signals. The wavelength demultiplexingsection wavelength demultiplexes the optical correlation signals, whichhave been outputted from the optical phase intensity conversion section,in accordance with wavelengths of the signals, and outputs resultantsignals as optical correlation signals. The optical-electricalconversion sections respectively convert the optical correlationsignals, which have been outputted from the wavelength demultiplexingsection, and respectively output resultant signals as correlationsignals. Each of the signal identification sections identifies one ofthe correlation signals outputted from a corresponding one of theoptical-electrical conversion sections, thereby detecting a data signal.

According to the second aspect of the present invention, optical phasemodulation is performed, in accordance with the template signal, on theoptical pulse signals respectively having different wavelengths whichhave been wavelength division multiplexed, and then resultant signalsare converted by the optical phase intensity conversion section into theoptical correlation signals. When the optical correlation signals areoutputted from the optical phase intensity conversion section, theoptical correlation signals are still wavelength division multiplexed.The wavelength division multiplexed optical correlation signals arewavelength demultiplexed in accordance with the wavelengths thereof bythe wavelength demultiplexing section. Thereafter, the opticalcorrelation signals are converted into electrical signals, and then datasignals are detected therefrom. In the second aspect, by using cyclicityof the optical phase intensity conversion section, the opticalcorrelation signals which are wavelength division multiplexed can beobtained. Thus, the ultra wideband communication system, which iscapable of performing wavelength division multiplexing and in which thenumber of component elements provided for correlation processing is notrequired to correspond to the number of wavelengths, is provided.

Preferably, an interval between each of wavelengths of the plurality ofoptical pulse signals is an integral multiple of a free spectrum rangeof the optical phase intensity conversion section.

As a result, optical-electrical conversion is performed when each ofoptical intensities of optical phase signals is optimal. Therefore, atransmission quality is expected to be optimally improved.

As one embodiment, the first optical phase modulation section mayperform optical phase modulation by an external modulation method.

As one embodiment, the first optical phase modulation section mayperform optical phase modulation by a direct modulation method.

As one embodiment, the optical phase intensity conversion section may bestructured by an interferometer.

Preferably, the optical phase intensity conversion section uses transferfactor characteristics, which are different from each other in relationto an optical phase of the optical phase demodulation signal, so as tooutput two optical correlation signals respectively having opticalintensities which are opposite to each other with respect to a referenceoptical intensity, and the optical-electrical conversion section isstructured by a bipolar photodiode to which the two optical correlationsignals are inputted.

As a result, a correlation signal, which has an amplitude changing toplus and also to minus with respect to the GND level, is obtained.Therefore, a data signal is easily detected.

As one embodiment, the optical phase intensity conversion section may bestructured by an optical filter.

As one embodiment, the optical phase intensity conversion section may bestructured by an adaptive photodetector.

As one embodiment, the second optical phase modulation section may bestructured by a spatial light phase modulator, and the opticaltransmission path may be a free space.

Preferably, the first optical phase modulation section performs, inaccordance with the pulse signal, phase modulation in either one of twomanners, in one of which the first optical phase modulation sectionperforms phase modulation such that an optical phase changes in adirection from 0 to π, and in another of which the first optical phasemodulation section performs phase modulation such that an optical phasechanges in a direction from π to 0, and the second optical phasemodulation section performs, in accordance with the template signalwhich is uniquely set, phase modulation in a predetermined mannerregardless of the data signal, the predetermined manner being either oneof two manners, in one of which the second optical phase modulationsection performs phase modulation such that an optical phase changes ina direction from 0 to π, and in another of which the second opticalphase modulation section performs phase modulation such that an opticalphase changes in a direction from π to 0.

As a result, the optical phase demodulation signal outputted from thesecond optical phase modulation section is: an optical phase signalwhose optical phase changes between 0 and π/2 in accordance withcorrelations with the template signal and the optical pulse signal; oran optical phase signal whose optical phase changes between π/2 and π inaccordance with correlations with the template signal and the opticalpulse signal. Consequently, the optical correlation signal whose opticalphase is in a range between 0 and π is obtained by using the opticalphase intensity conversion section, from which the optical correlationsignal having an optical intensity continuously changing is outputted.Thus, correlation processing is performed appropriately.

A third aspect of the present invention is an optical transmissiondevice used in an ultra wideband communication system for converting apulse signal into an optical pulse signal, transmitting the opticalpulse signal, and demodulating the transmitted optical pulse signal, thedevice comprising: a pulse generation section for generating the pulsesignal based on a data signal; and an optical phase modulation sectionfor, in accordance with the pulse signal generated by the pulsegeneration section, performing optical phase modulation, and outputtinga resultant signal as an optical pulse signal. The optical phasemodulation section performs phase modulation in either one of twomanners, in one of which the optical phase modulation section performsphase modulation so as to cause an optical phase to change in adirection from 0 to π, and in another of which the optical phasemodulation section performs phase modulation so as to cause an opticalphase to change in a direction from π to 0, such that: after the opticalpulse signal is propagated through the optical transmission path,optical phase modulation is performed on the optical pulse signal inaccordance with a predetermined template signal having a correlationwith the pulse signal, in order for the optical pulse signal to beconverted into an optical phase demodulation signal; information aboutan optical phase of the optical phase demodulation signal is convertedinto information about an optical intensity thereof, in order for theoptical phase demodulation signal to be converted into an opticalcorrelation signal; and optical-electrical conversion is performed onthe optical correlation signal in order for the optical correlationsignal to be converted into a correlation signal.

According to the third aspect of the present invention, the opticaltransmission device capable of improving a quality of correlationprocessing is provided.

A fourth aspect of the present invention is an optical reception deviceused in an ultra wideband communication system for converting a pulsesignal into an optical pulse signal, transmitting the optical pulsesignal, and demodulating the transmitted optical pulse signal, thedevice comprising: a template generation section for generating a pulsewhich has a correlation with the pulse signal and which has apredetermined waveform, and outputting the pulse as a template signal;an optical phase modulation section for, in accordance with the templatesignal outputted from the template generation section, performingoptical phase modulation on the optical pulse signal, on which opticalphase modulation has been performed such that an optical phase of theoptical pulse signal changes in a direction from 0 to π, or in adirection from π to 0, and for outputting a resultant signal as anoptical phase demodulation signal; an optical phase intensity conversionsection for converting information about an optical phase of the opticalphase demodulation signal outputted from the optical phase modulationsection into information about an optical intensity thereof, andoutputting a resultant signal as anoptical correlation signal; anoptical-electrical conversion section for performing optical-electricalconversion on the optical correlation signal outputted from the opticalphase intensity conversion section, and outputting a resultant signal asa correlation signal; and a signal identification section for detectinga data signal by identifying the correlation signal outputted from theoptical-electrical conversion section.

According to the fourth aspect of the present invention, the opticalreception device capable of improving a quality of correlationprocessing is provided.

A fifth aspect of the present invention is an optical repeater used inan ultra wideband communication system for performing wavelengthdivision multiplexing of a plurality of optical pulse signals, on eachof which optical phase modulation has been performed in accordance witha plurality of pulse signals, transmitting the plurality of opticalpulse signals, and wavelength demultiplexing the plurality oftransmitted optical pulse signals to demodulate the optical pulsesignals. The optical pulse signals are signals, on each of which opticalphase modulation has been performed such that an optical phase of eachof the optical pulse signals changes in a direction from 0 to π, or in adirection from π to 0. The optical repeater comprises: a templategeneration section for generating a pulse which has a correlation witheach of the pulse signals and which has a predetermined waveform, andoutputting the pulse as a template signal; an optical phase modulationsection for, in accordance with the template signal outputted from thetemplate generation section, performing optical phase modulation on theplurality of optical pulse signals which have been wavelength divisionmultiplexed, and outputting resultant signals as optical phasedemodulation signals which have been wavelength division multiplexed;and an optical phase intensity conversion section for convertinginformation about an optical phase of each of the optical phasedemodulation signals, which have been wavelength division multiplexedand which have been outputted from the optical phase modulation section,into information about an optical intensity thereof, and outputtingresultant signals as optical correlation signals having been wavelengthdivision multiplexed.

According to the fifth aspect of the present invention, optical phasemodulation is performed on wavelength division multiplexed optical pulsesignals, while the signals are kept wavelength division multiplexed, andas a result, wavelength division multiplexed optical phase demodulationsignals are obtained. Further, optical phases of the wavelength divisionmultiplexed optical phase demodulation signals are converted intooptical intensities, and as a result, wavelength division multiplexedoptical correlation signals are obtained. Thus, the optical repeater,which is used in the ultra wideband communication system and which isnot required to have the number of optical devices corresponding to thenumber of wavelengths, is provided.

Effect of the Invention

In the ultra wideband communication device according to the presentinvention, an optical device, by which a wideband frequencycharacteristic is obtained more easily than by a conventional correlator(electrical mixer), can be used, and thereby a quality of correlationprocessing is improved. When wavelength division multiplexing isperformed, the cyclicity of the transfer factor characteristic of theinterferometer is used so that the optical device can be commonly used.This reduces the number of component elements within the ultra widebandcommunication device, and thereby improving applicability of the ultrawideband communication device for wavelength division multiplexing.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a block diagram showing a configuration of an ultrawideband communication system 1 according to a first embodiment of thepresent invention.

[FIG. 2A] FIG. 2A shows relationships between an optical phase of anoptical pulse signal and time.

[FIG. 2B] FIG. 2B illustrates a manner of obtaining an opticalcorrelation signal based on the optical pulse signal and a templatesignal.

[FIG. 2C] FIG. 2C shows relationships between an optical phase of anoptical phase demodulation signal and time.

[FIG. 2D] FIG. 2D is a graph showing a transfer factor of aninterferometer 23 in relation to an optical phase of a signal.

[FIG. 2E] FIG. 2E shows relationships between an optical intensity of anoptical correlation signal and time.

[FIG. 3A] FIG. 3A shows a change occurring over time in a continuouslight outputted from a light source 11.

[FIG. 3B] FIG. 3B shows amplitude changes of pulse signals outputtedfrom a pulse generation section 13.

[FIG. 3C] FIG. 3C shows optical phase changes of the optical pulsesignals outputted from a first optical phase modulation section 12.

[FIG. 4A] FIG. 4A shows an amplitude change of the template signal.

[FIG. 4B] FIG. 4B shows optical phase changes of optical phasedemodulation signals outputted from a second optical phase modulationsection 21.

[FIG. 4C] FIG. 4C shows changes in an optical intensity of the opticalcorrelation signal outputted from the interferometer 23.

[FIG. 4D] FIG. 4D shows amplitude changes of correlation signalsoutputted from an optical-electrical conversion section 24.

[FIG. 5] FIG. 5 is a block diagram showing a configuration of an ultrawideband communication system 2 according to a second embodiment of thepresent invention.

[FIG. 6A] FIG. 6A shows relationships between time and an optical phaseof the optical pulse signal.

[FIG. 6B] FIG. 6B illustrates a manner of obtaining the opticalcorrelation signal based on the optical pulse signal and the templatesignal.

[FIG. 6C] FIG. 6C shows relationships between time and an optical phaseof the optical phase demodulation signal.

[FIG. 6D] FIG. 6D is a graph showing a transfer factor at an outputterminal A of an interferometer 33 in relation to a phase of a signal.

[FIG. 6E] FIG. 6E shows a graph showing a transfer factor at an outputterminal B of the interferometer 33 in relation to a phase of a signal.

[FIG. 6F] FIG. 6F shows relationships between time and an opticalintensity of an optical correlation signal c outputted from the outputterminal A.

[FIG. 6G] FIG. 6G shows relationships between time and an opticalintensity of an optical correlation signal d outputted from the outputterminal B.

[FIG. 6H] FIG. 6H shows a change occurring over time in the correlationsignal outputted from an optical-electrical conversion section 34 in thecase where a data signal is “10”.

[FIG. 7] FIG. 7 shows a configuration of an ultra wideband communicationsystem 3 according to a third embodiment of the present invention.

[FIG. 8] FIG. 8 is a block diagram showing a configuration of an ultrawideband communication system 4 according to a fourth embodiment of thepresent invention.

[FIG. 9A] FIG. 9A is a block diagram showing an ultra widebandcommunication system as a result of: extracting, from a conventionalultra wideband communication system disclosed in a patent document 1,component elements relating to the present invention; and adding, to theextracted component elements, component elements required for opticaltransmission which are disclosed in International Publication WO2004/082175.

[FIG. 9B] FIG. 9B shows waveforms of pulse signals outputted from apulse generation section 92.

[FIG. 9C] FIG. 9C shows waveforms of optical pulse signals outputtedfrom an electrical-optical conversion section 93.

DESCRIPTION OF THE REFERENCE CHARACTERS

1, 2, 3, 4 ultra wideband communication systems

1 a, 3 a, 4 optical transmission devices

1 b, 3 b, 4 b optical reception devices

3 c, 14 optical transmission paths

4 c optical repeater

10, 40 optical modulation sections

10-1 to 10-n first to nth optical modulation sections

11 light source

12 first optical phase modulation section

13, 43 pulse generation sections

20, 30, 50 optical demodulation sections

20-1 to 20-n first to nth optical demodulation sections

21 second optical phase modulation section

21-1 to 21-n first to nth optical demodulation sections

22, 47, 52 template generation sections

23, 33, 48 interferometers

24, 34 optical-electrical conversion sections

25, 35, 55 signal identification sections

45 wavelength division multiplexing section

41 array light source

46 second optical phase modulation section

42 array first spatial light phase modulation section

44 wavelength demultiplexing section

51 array second spatial light phase modulation section

53 interferometry section

54 array optical-electrical conversion section

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

FIRST EMBODIMENT

FIG. 1 is a block diagram showing a configuration of an ultra widebandcommunication system 1 according to a first embodiment of the presentinvention. In FIG. 1, the ultra wideband communication system 1comprises an optical transmission device 1 a, an optical transmissionpath 14 and an optical reception device 1 b. The optical transmissiondevice 1 a includes an optical modulation section 10. The opticalreception device 1 b includes an optical demodulation section 20. A datasignal is transmitted from the optical modulation section 10 to theoptical demodulation section 20 via the optical transmission path 14.The optical modulation section 10 includes a light source 11, a firstoptical phase modulation section 12 and a pulse generation section 13.The optical demodulation section 20 includes a second optical phasemodulation section 21, a template generation section 22, aninterferometer 23 which is an optical phase intensity conversionsection, an optical-electrical conversion section 24 and a signalidentification section 25.

The optical modulation section 10 converts an electrical pulse signal,which is generated based on a data signal to be transmitted(hereinafter, the electrical pulse signal will be simply referred to asa pulse signal), into a light pulse signal (hereinafter, the light pulsesignal will be referred to as an optical pulse signal), and outputs theoptical pulse signal. The optical pulse signal outputted from theoptical modulation section 10 is propagated through the opticaltransmission path 14, and inputted into the optical demodulation section20. The optical demodulation section 20 demodulates the propagatedoptical pulse signal to obtain the original data signal.

Operations performed in the first embodiment of the present inventionwill be described below. In the optical modulation section 10, the lightsource 11 emits a continuous light. The pulse generation section 13generates a pulse signal based on a data signal to be transmitted. Thefirst optical phase modulation section 12 performs, in accordance withthe pulse signal outputted from the pulse generation section 13, opticalphase modulation on the light from the light source 11, and outputs aresultant signal as an optical pulse signal a (for details, refer tolater-described FIG. 2A). Hereinafter, an optical phase modulationprocess performed by the first optical phase modulation section 12 willbe referred to as a first optical phase modulation process.

The optical transmission path 14 propagates the optical pulse signal aoutputted from the first optical phase modulation section 12.

In the optical demodulation section 20, the template generation section22 generates, in accordance with a synchronization timing outputted fromthe later-described signal identification section 25, a predeterminedpulse having a correlation with the pulse signal outputted from thepulse generation section 13, and outputs the pulse as a template signal.Here, having a correlation with the pulse signal means that an amplitudeof the template signal changes in a same direction as that of anamplitude change of the pulse signal, or that the amplitude of thetemplate signal changes in an opposite direction to that of theamplitude change of the pulse signal. The second optical phasemodulation section 21 performs, in accordance with the template signaloutputted from the template generation section 22, optical phasemodulation on the optical pulse signal having propagated through theoptical transmission path 14, and outputs a resultant signal as anoptical phase demodulation signal b. The interferometer 23 may bestructured by, e.g., a Mach-Zehnder interferometer. The interferometer23 changes information about an optical phase of the optical phasedemodulation signal b outputted from the second optical phase modulationsection 21 (hereinafter, referred to as optical phase demodulationinformation) into information about an optical intensity thereof(hereinafter, referred to as optical intensity modulation information),and outputs a resultant signal as an optical correlation signal c. Theoptical-electrical conversion section 24 performs optical-electricalconversion of the optical correlation signal c outputted from theinterferometer 23, and outputs a resultant signal as a correlationsignal. The signal identification section 25 identifies the correlationsignal outputted from the optical-electrical conversion section 24,thereby detecting the data signal transmitted from the opticalmodulation section 10.

Note that, the signal identification section 25 detects thesynchronization timing for detecting the data signal, and inputs thesynchronization timing into the template generation section 22. Anexemplary manner of detecting the synchronization timing is that thesignal identification section 25 sweeps, in a time direction, thetemplate signal outputted from the template generation section 22, andintegrates the correlation signal over a predetermined time cycle (e.g.,a time cycle of the template signal), and then outputs a timing, atwhich an integration value becomes greatest, as the synchronizationtiming. A manner of detecting the synchronization timing is not limitedthereto. The synchronization timing maybe inputted into the templategeneration section 22 from a function block which is different from thesignal identification section 25.

FIG. 2A shows relationships between an optical phase of the opticalpulse signal and time. As shown in FIG. 2A, the optical pulse signalcorresponding to data “1” is a signal whose optical phase changes fromπ/4 to 0 to π, and then returns from π to π/4. Also, the optical pulsesignal corresponding to data “0” is a signal whose optical phase changesfrom π/4 to π to 0, and then returns from 0 to π/4. To be specific,there are two cases: in one of which the first optical phase modulationsection 12 performs, in accordance with the data signal, i.e., the pulsesignal, optical phase modulation such that the optical phase of theoptical pulse signal changes in a direction from 0 to π; and in theother of which the first optical phase modulation section 12 performs,in accordance with the data signal, i.e., the pulse signal, opticalphase modulation such that the optical phase of the optical pulse signalchanges in a direction from π to 0.

Here, it is assumed that the template signal used for optical phasemodulation has a same phase change as that of the optical pulse signalcorresponding to the data “1”. In other words, the template signal has aphase changing from π/4 to 0 to π, and then returns from π to π/4.Hereinafter, phase modulation performed in accordance with the templatesignal will be referred to as a second phase modulation process(template process).

FIG. 2B illustrates a manner of obtaining the optical correlation signalbased on the optical pulse signal and template signal. As shown in FIG.2B, when optical phase modulation is performed, in accordance with thetemplate signal, on the optical pulse signal corresponding to the data“1”, the optical phase of the optical correlation signal is the sum ofthe optical phases of the optical pulse signal and an optical signalwhich results from the second phase modulation process. Similarly, whenoptical phase modulation is performed, in accordance with the templatesignal, on the optical pulse signal corresponding to the data “0”, theoptical phase of the optical correlation signal is the sum of theoptical phases of the optical pulse signal and an optical signal whichresults from the second phase modulation process.

FIG. 2C shows relationships between an optical phase of the opticalphase demodulation signal and time. As a result of the additioncalculations shown in FIG. 2B, the optical phase demodulation signal,whose optical phase has either one of the relationships with time asshown in FIG. 2C, is outputted from the second optical phase modulationsection 21.

FIG. 2D is a graph showing a transfer factor of the interferometer 23 inrelation to an optical phase of a signal. As shown in FIG. 2D, thetransfer factor of the interferometer 23 changes in accordance with theoptical phase. The interferometer 23 functions as the optical phaseintensity conversion section for converting the optical phase into anoptical intensity.

FIG. 2E shows relationships between an optical intensity of the opticalcorrelation signal and time. When the optical phase demodulation signalhaving either one of the optical phases shown in FIG. 2C is inputtedinto the interferometer 23 having the transfer factor shown in FIG. 2D,a light having an intensity corresponding to said either one of theoptical phases is outputted as the optical correlation signal from theinterferometer 23 as shown in FIG. 2E. A transfer factor characteristicof the interferometer 23 illustrated in FIG. 2D shows that the closer to0 the optical phase is, the higher is the transfer factor, and thecloser to π the optical phase is, the lower is the transfer factor.Accordingly, as shown in FIG. 2E, an optical phase, which is equal to orsmaller than π/2,of the optical phase demodulation signal correspondingto the data signal “1” corresponds to an optical intensity changingbetween ½ and 1 (here, ½ and 1 are relative values), and an opticalphase, which is equal to or greater than π/2,of the optical phasedemodulation signal corresponding to the data signal “0” corresponds toan optical intensity changing between 0 and ½.

Next, operations of the ultra wideband communication system 1 will bedescribed by using specific exemplary data. Here, it is assumed that adata signal to be transmitted is “10”.

FIG. 3A shows a change occurring over time in a continuous lightoutputted from the light source 11. As shown in FIG. 3A, an intensity ofthe continuous light remains same as the time passes.

FIG. 3B shows amplitude changes of pulse signals outputted from thepulse generation section 13. As shown in FIG. 3B, the pulse generationsection 13 outputs, for the data signal “1”, a pulse signal whoseamplitude changes from minus to plus, and outputs, for the data signal“0”, a pulse signal whose amplitude changes from plus to minus.

FIG. 3C shows optical phase changes of optical pulse signals outputtedfrom the first optical phase modulation section 12. The first opticalphase modulation section 12 converts information about the amplitude ofthe pulse signal into optical phase information, and then outputs aresultant signal as the optical pulse signal. Accordingly, as shown inFIGS. 3B and 3C, the pulse signal and optical pulse signal have a samepolarity.

FIG. 4A shows the amplitude change of the template signal. As shown inFIG. 4A, the template signal has a same polarity as that of the pulsesignal corresponding to the data signal “1”. The template signal is asignal having a predetermined polarity which is fixed regardless of acontent of a data signal.

FIG. 4B shows optical phase changes of optical phase demodulationsignals outputted from the second optical phase modulation section 21.The template signal has a polarity which is uniquely predetermined to besame as that of the pulse signal corresponding to the data signal “1”.In accordance with the template signal having the uniquely predeterminedpolarity, the second optical phase modulation section 21 performs phasemodulation on a signal inputted thereto, such that, regardless of thecontent of the data signal, the optical phase of the inputted signalchanges in the direction from 0 to π. Accordingly, in the case where theoptical pulse signal has a same polarity as that of a signal used toperform the second phase modulation process, the second optical phasemodulation section 21 outputs the optical phase demodulation signalhaving optical phase information changing between π/2 and 0. Whereas, inthe case where the optical pulse signal has a different polarity fromthat of the signal used to perform the second phase modulation process,the second optical phase modulation section 21 outputs the optical phasedemodulation signal having an optical phase changing between π/2 and π.This means that the second optical phase modulation section 21 hasadded, as shown in the addition calculations of FIG. 2B, optical phaseinformation about the optical pulse signal to optical phase informationabout the signal used for the second phase modulation process.

FIG. 4C shows changes in an optical intensity of the optical correlationsignal outputted from the interferometer 23. As shown in FIG. 2D, thetransfer factor of the interferometer 23 changes in accordance with anoptical phase of a signal. Accordingly, the interferometer 23 convertsoptical phase information about the optical phase demodulation signalinto optical intensity information, and outputs a resultant signal asthe optical correlation signal, whose light intensity is represented bya relative light intensity and which has a relative optical intensitywaveform.

FIG. 4D shows amplitude changes of correlation signals outputted fromthe optical-electrical conversion section 24. It is assumed in FIG. 4Dthat a single photodiode (single-PD) is used as the optical-electricalconversion section 24. As shown in FIG. 4D, when the single photodiodeis used as the optical-electrical conversion section 24, a correlationsignal, whose amplitude changes within a range higher than the GND levelin accordance with the optical intensity of the optical correlationsignal, is outputted. The correlation signal corresponding to the datasignal “1” is a high-level signal, and the correlation signalcorresponding to the data signal “0” is a low-level signal.

The signal identification section 25 integrates the correlation signalover a predetermined time cycle (e.g., a time cycle of the templatesignal), and then compares an integration value of the correlationsignal with that of the high-level signal and low-level signal, therebyrecognizing whether the data signal transmitted from the opticalmodulation section 10 is “1” or “0”.

As described above, according to the first embodiment, optical phasemodulation is performed twice, i.e., the first optical phase modulationsection 12 performs optical phase modulation on the pulse signal tooutput a resultant signal as the optical pulse signal, and the secondoptical phase modulation section 21 performs optical phase demodulationon the optical pulse signal in accordance with the template signal. As aresult, the sum of the optical phases of the optical pulse signal and anoptical signal which results from the second phase modulation process isoutputted as the optical phase demodulation signal. When the opticalpulse signal outputted from the optical modulation section 10 has areverse characteristic corresponding to that of the data signal, theoptical phase demodulation signal to be outputted, which is the sum ofthe optical phases of the optical pulse signal and the template signal,also has the reverse characteristic. When optical phase intensityconversion is performed, by using the interferometer 23, on the opticalphase demodulation signal, and the signal is converted into an opticalintensity, the original data signal can be identified by using theoptical-electrical conversion section 24 and the signal identificationsection 25. Thus, in the ultra wideband communication system accordingto the first embodiment, the original data signal can be identified byperforming correlation processing with an optical device. Consequently,a quality of correlation processing improves as compared withconventional correlation processing performed by multiplying electricalamplitudes.

In the first embodiment, an external modulation method has beendescribed in which the first optical phase modulation section modulatesthe optical phase of the continuous light emitted from the light source.However, optical phase modulation may be performed by a directmodulation method.

Further, in the first embodiment, a pulse corresponding to the datasignal “1” is used as the template signal. However, a pulsecorresponding to the data signal “0” may be used as the template signal.In such a case, the second optical phase modulation section 21 performs,in accordance with the template signal having a uniquely determinedpolarity, phase modulation such that the optical phase of an inputtedsignal changes in a direction from π to 0 regardless of the data signal.Although some signals have opposite polarities to those of the othersignals, phase modulation is performed for each signal in a same manneras that described above.

Although the interferometer 23 is used as the optical phase intensityconversion section in the first embodiment, an optical filter, anadaptive photodetector or the like may be used as the optical phaseintensity conversion section. In other words, used as the optical phaseintensity conversion section may be an optical device capable ofoutputting an optical signal which has an optical intensitycorresponding to an optical phase of an optical signal inputted to theoptical device. The adaptive photodetector is described in detail in thefollowing document: Celis, M.; Hernandez, D.; Rodriguez, P.; Stepanov,S.; Korneev, N., “Polarization-independent linear detection of opticalphase modulation using photo-emf adaptive photodetectors”, TechnicalDigest. Summaries of papers presented at the Conference on Lasers andElectro-Optics(CLEO) 98., 1998, 3-8 May 1998 Page(s):530-531.

SECOND EMBODIMENT

FIG. 5 is a block diagram showing a configuration of an ultra widebandcommunication system 2 according to a second embodiment of the presentinvention. In FIG. 5, component elements which are identical with thoseof the first embodiment are denoted by same reference numerals as thoseused for the component elements of the first embodiment, and detaileddescriptions thereof will be omitted. The optical demodulation section30 according to the second embodiment comprises the second optical phasemodulation section, the template generation section 22, aninterferometer 33, an optical-electrical conversion section 34 and asignal identification section 35.

FIG. 6A shows relationships between time and an optical phase of anoptical pulse signal. FIG. 6B illustrates a manner of obtaining anoptical correlation signal based on an optical pulse signal and atemplate signal. FIG. 6C shows relationships between time and an opticalphase of the optical phase demodulation signal. FIGS. 6A to 6C areidentical with FIGS. 2A to 2C of the first embodiment.

The interferometer 33 has two output terminals. In response to aninputted optical phase demodulation signal, the interferometer 33generates pieces of optical intensity modulation information which arein opposite phase to each other, and then outputs two opticalcorrelation signals c and d. The interferometer 33 maybe a Mach-Zehnderinterferometer, for example. Here, the pieces of optical intensitymodulation information being in opposite phase to each other means thatwhen optical intensity changes, each of which corresponds to an opticalphase of the inputted optical phase demodulation signal, are representedby waveforms as shown in FIGS. 6D and 6E, the waveforms are in oppositephase. In other words, the interferometer 33 converts, by using twotransfer factor characteristics which are opposite to each other, apiece of optical phase modulation information about the inputted opticalphase demodulation signal into two pieces of optical intensitymodulation information. As a result, the interferometer 33 outputs twooptical correlation signals (refer to later-described FIGS. 6F and 6G)respectively having pieces of optical intensity information which areopposite to each other. Here, the pieces of optical intensityinformation, which are opposite to each other, respectively representoptical intensities respectively having polarities which are opposite toeach other with respect to a particular reference optical intensity(e.g., ½ in FIGS, 6F and 6G).

The optical-electrical conversion section 34 is structured by a bipolarphotodiode.

FIG. 6D is a graph showing, in relation to a phase of a signal, atransfer factor at an output terminal A of the interferometer 33. FIG.6E is a graph showing, in relation to a phase of a signal, a transferfactor at an output terminal B of the interferometer 33. FIG. 6F showsrelationships between time and an optical intensity of the opticalcorrelation signal c outputted from the output terminal A. FIG. 6G showsrelationships between time and an optical intensity of the opticalcorrelation signal d outputted from the output terminal B.

As shown in FIGS. 6D and 6E, the interferometer 33 has two transferfactor characteristics which are opposite to each other. By usingoptical phase dependency of a transfer factor (A), the interferometer 33outputs an optical phase demodulation signal inputted from the outputterminal A as the optical correlation signal c. By using optical phasedependency of a transfer factor (B), the interferometer 33 outputs theoptical phase demodulation signal inputted from the output terminal B asthe optical correlation signal d. A relationship between FIG. 6D andFIG. 6F is same as that between FIG. 2D and FIG. 2E. The transfer factorcharacteristic illustrated in FIG. 6E shows that the closer to 0 thephase of a signal is, the lower is the transfer factor, and the closerto π the phase is, the higher is the transfer factor. Accordingly, asshown in FIG. 6G, a phase, which is equal to or smaller than π/2, of theoptical phase demodulation signal corresponding to the data signal “1”corresponds to an optical intensity changing between 0 and ½, and aphase, which is equal to or greater than π/2, of the optical phasedemodulation signal corresponding to the data signal “0” corresponds toan optical intensity changing between ½ and 1.

FIG. 6H shows a change occurring over time in the correlation signaloutputted from the optical-electrical conversion section 34 in the casewhere the data signal is “10”. Here, a bipolar photodiode is used as theoptical-electrical conversion section 34. Since the optical correlationsignals shown in FIGS. 6F and 6G are inputted into theoptical-electrical conversion section 34, the correlation signal has anamplitude changing to plus and also to minus with respect to the GNDlevel.

The signal identification section 35 identifies the original data signalbased on whether the amplitude of the correlation signal is in plus orminus with respect to the GND level. Thus, the correlation signal ismore easily identified as compared with the first embodiment, andtherefore a quality of identification is improved.

As described above, according to the second embodiment, the opticaldemodulation section 30 converts an optical phase of an inputted opticalphase demodulation signal into two optical intensities respectivelyhaving polarities which are opposite to each other with respect to aparticular reference optical intensity, thereby converting the inputtedoptical phase demodulation signal into two optical correlation signals,and then the two optical correlation signals are converted into anelectrical signal by using a bipolar photodiode. This makes it possibleto obtain a correlation signal having a polarity whose center is locatedat the GND level. For this reason, the signal identification section 35can easily identify the correlation signal. This improves the quality ofidentification.

In the second embodiment, the interferometer 33 is used as the opticalphase intensity conversion section. However, the present embodiment isnot limited thereto. Used as the optical intensity conversion sectionmay be an optical filter, an adaptive photodetector or the like which iscapable of converting an optical phase of a signal into two opticalintensities respectively having polarities which are opposite to eachother with respect to a particular reference optical intensity, therebyconverting the signal into two optical correlation signals.

Also in the second embodiment, the first optical phase modulationsection may perform optical phase modulation by a direct modulationmethod, and a pulse corresponding to the data signal “0” may be used asthe template signal.

THIRD EMBODIMENT

FIG. 7 shows a configuration of an ultra wideband communication system 3according to a third embodiment of the present invention. In FIG. 7, theultra wideband communication system 3 comprises an optical transmissiondevice 3 a, an optical reception device 3 b and an optical transmissionpath 3 c which is a free space. The optical transmission device 3 aincludes an optical modulation section 40. The optical modulationsection 40 includes an array light source 41, an array first spatiallight phase modulation section 42 and a pulse generation section 43. Theoptical reception device 3 b includes an optical demodulation section50. The optical demodulation section 50 includes an array second spatiallight phase modulation section 51, a template generation section 52, aninterferometry section 53, an array optical-electrical conversionsection 54 and a signal identification section 55.

The array light source 41 has a plurality of light sources (FIG. 7illustratively shows three light sources) respectively outputtingcontinuous lights (FIG. 7 illustratively shows first to third continuouslights).

The pulse generation section 43 outputs pulse signals based on datasignals to be transmitted. Here, each pulse signal is same as that ofthe first embodiment.

The array first spatial light phase modulation section 42 has aplurality of spatial light phase modulation sections respectivelycorresponding to the light sources, and performs, in accordance with thepulse signals, phase modulation respectively on the continuous lights(FIG. 7 shows the first to third continuous lights) so as to outputresultant signals to the free space as optical pulse signals. Eachoptical pulse signal is same as that of the first embodiment. JapanesePatent Application No. 2004-295343 describes a spatial light phasemodulation section in detail. For example, there has been a spatiallight phase modulator using crystal liquid. To be more specific, therehas been a liquid crystal spatial light modulator called PAL-SLMmanufactured by Hamamatsu Photonics K.K.

The optical pulse signals outputted from the array first spatial lightphase modulation section propagate through the free space which is theoptical transmission path 3 c, and enter the array second spatial lightphase modulation section 51. The array second spatial light phasemodulation section 51 has a plurality of spatial light phase modulationsections, and performs, in accordance with template signals outputtedfrom the template generation section 52, optical phase modulationrespectively on the optical pulse signals so as to output resultantsignals as a plurality of optical phase demodulation signals. Eachoptical phase demodulation signal is same as that of the firstembodiment.

The interferometry section 53 converts pieces of information aboutoptical phases of the optical phase demodulation signals into pieces ofinformation about optical intensities thereof, and outputs resultantsignals as optical correlation signals. Each of the optical correlationsignals is same as that of the first embodiment.

The array optical-electrical conversion section 54 converts the opticalcorrelation signals into electrical signals, and outputs the electricalsignals as correlation signals. Each of the correlation signals is sameas that of the first embodiment.

The signal identification section 55 identifies the correlation signals.A manner of identifying the signals is same as that of the firstembodiment.

As described above, the first and second optical phase modulationsections maybe spatial light phase modulation sections. Transmission ofdata signals maybe performed even with the optical transmission pathwhich is a free space. By using such spatial light phase modulationsections, only an optical phase of an optical signal transmitted via thefree space can be modulated without changing an amplitude of the opticalsignal. Since correlation processing is performed on a plurality ofoptical pulse signals by using same template signals, synchronizationsbetween the template signals and the plurality of optical pulse signalsare unified.

Similarly to the second embodiment, an optical phase intensityconversion section may be used instead of the interferometry section 53,the optical phase intensity conversion section being capable ofconverting an optical phase of each of the optical phase demodulationsignals, by using transfer factor characteristics which are opposite toeach other in relation to the optical phase, into two opticalintensities respectively having polarities which are opposite to eachother with respect to a particular reference optical intensity, therebyconverting each of the optical phase demodulation signals into twooptical correlation signals. In such a case, each optical-electricalconversion section in the array optical-electrical conversion section 54may be structured by a bipolar photodiode.

FOURTH EMBODIMENT

FIG. 8 is a block diagram showing a configuration of an ultra widebandcommunication system 4 according to a fourth embodiment of the presentinvention. The ultra wideband communication system shown in FIG. 8 isthe ultra wideband communication system according to the firstembodiment which is used for wavelength division multiplexedcommunications. In FIG. 8, component elements having same functions asthose of the ultra wideband communication system shown in FIG. 1 aredenoted by same reference numerals as those used for the componentelements of the ultra wideband communication system shown in FIG. 1, anddetailed descriptions thereof will be omitted.

In FIG. 8, the ultra wideband communication system 4 comprises anoptical transmission device 4 a, an optical repeater 4 c, an opticalreception device 4 b and an optical transmission path 14 providedbetween the optical repeater 4 c and the optical transmission device 4a. The optical transmission device 4 a includes first to nth opticalmodulation sections 10-1 to 10-n and a wavelength division multiplexingsection 45. The optical repeater 4 c includes a second optical phasemodulation section 46, a template generation section 47 and aninterferometer 48. The optical reception device 4 b includes first tonth optical demodulation sections 20-1 to 20-n and a wavelengthdemultiplexing section 44.

The first to nth optical modulation sections 10-1 to 10-n respectivelyoutput first to nth optical pulse signals respectively having differentwavelengths. Each of the optical pulse signals is same as that of thefirst embodiment except that each of the optical pulse signals has adifferent wavelength. Here, an interval between each wavelength is anintegral multiple of a free spectrum range (FSR) of an interferometer48.

The wavelength division multiplexing section 45 performs wavelengthdivision multiplexing of the first to nth optical pulse signalsoutputted from the first to nth optical modulation sections 10-1 to10-n.

The optical transmission path 14 propagates the first to nth opticalpulse signals which have been wavelength division multiplexed at thewavelength division multiplexing section 45.

The template generation section 47 generates a predetermined pulsecorrelated to the optical pulse signals outputted from the first to nthoptical modulation sections 10-1 to 10-n, and outputs the predeterminedpulse as a template signal.

The second optical phase modulation section 46 performs, in accordancewith the template signal outputted from the template generation section47, optical phase modulation on the first to nth optical pulse signalshaving propagated through the optical transmission path 14, and outputsresultant signals as the first to nth optical phase demodulationsignals. Here, a feature of the present embodiment is that a phase ofeach of the first to nth optical pulse signals is modulated as a resultof performing, in accordance with one template signal, optical phasemodulation on the first to nth optical pulse signals which have beenwavelength division multiplexed. The first to nth optical phase signalsoutputted from the second optical phase modulation section 46 are stillwavelength division multiplexed.

The interferometer 48 converts optical phase modulation informationabout the first to nth optical phase demodulation signals outputted fromthe second optical phase modulation section 46 into optical intensitymodulation information, and output resultant signals as first to nthoptical correlation signals. The first to nth optical phase demodulationsignals are wavelength division multiplexed before the signals areinputted into the interferometer 48, and, in accordance with cyclicityof the transfer factor characteristic of the interferometer 48, anoptical phase of each of the first to nth optical phase demodulationsignals is changed into an optical intensity corresponding to theoptical phase. As a result, the optical phase demodulation signals areconverted into the optical correlation signals. When the first to nthoptical correlation signals are outputted from the interferometer 48,the signals are still wavelength division multiplexed. Here, referred toas the above-mentioned cyclicity is that a transfer factor of theinterferometer 48 in relation to a wavelength of each signal inputtedinto the interferometer 48 cyclically reaches its peak. The wavelengthof each signal inputted into the interferometer 48 maybe set at a mostappropriate wavelength in accordance with such a cycle. In other words,an interval between each wavelength may be set as an integral multipleof the free spectrum range (FSR) of the interferometer 48. This allows alight to be transmitted with a maximum transfer factor. As a result,each of the optical correlation signals, which arrive theoptical-electrical conversion sections 24, has a maximum opticalintensity. Thus, each of the optical correlation signals has an optimalquality.

The wavelength demultiplexing section 44 wavelength demultiplexes thefirst to nth optical correlation signals, which have been outputted fromthe interferometer 48, in accordance with the wavelengths thereof.

The first to nth optical demodulation sections 20-1 to 20-n respectivelycorrespond to the first to nth optical correlation signals which arewavelength demultiplexed in accordance with the wavelengths thereof atthe wavelength demultiplexing section 44. In the first opticaldemodulation section 20-1, the optical-electrical conversion section 24performs optical-electrical conversion on the first optical correlationsignal, and outputs a resultant signal as a correlation signal. Thesignal identification section 25 identifies the correlation signaloutputted from the optical-electrical conversion section 24, therebydetecting a data signal transmitted from a corresponding opticalmodulation section. Each of the second to nth optical demodulationsections 20-2 to 20-n operates in a same manner as that of the firstoptical demodulation section 20-1.

Signals subjected to optical phase modulation and optical phasedemodulation in the present embodiment are same as those of the firstembodiment which are shown in FIGS. 2A to 4D. However, as describedabove, the first to nth optical pulse signals respectively havedifferent wavelengths; the first to nth optical phase demodulationsignals respectively have different wavelengths; and the first to nthoptical correlation signals respectively have different wavelengths.

As described above, in the fourth embodiment, correlation processing isperformed by using the cyclicity of the transfer factor characteristicof the interferometer while keeping signals wavelength divisionmultiplexed. This eliminates the necessity that the system has thenumber of component elements for correlation processing whichcorresponds to the number of wavelengths of the signals. This prevents adevice for the system from increasing in size. Thus, the ultra widebandcommunication system, which is capable of performing wavelength divisionmultiplexing, is provided.

Preferably, an interval between each of wavelengths of the first to nthoptical pulse signals is an integral multiple of a free spectrum rangeof the optical phase intensity conversion section. Here, the freespectrum range of the optical phase intensity conversion section meansone cycle during which a transfer factor of the optical phase intensityconversion section becomes maximum in relation to a wavelength of asignal. In other words, it is preferred that each of the wavelengths ofthe first to nth optical pulse signals is located at where the transferfactor of the optical phase intensity conversion section becomesmaximum. By locating each wavelength in such a manner,optical-electrical conversion is performed when each of opticalintensities of the first to nth optical correlation signals is optimal.Therefore, a transmission quality is expected to be optimally improved.Note that, in the present invention, a manner of setting an intervalbetween each wavelength is not limited to the above since correlationprocessing can still be performed even if each wavelength is not locatedin such a manner.

The system maybe configured such that the second optical phasemodulation section, the template generation section and theinterferometer are provided for each wavelength. Alternatively, thesystem may be configured such that wavelength division multiplexing isperformed on only some of the optical pulse signals, and the secondoptical phase modulation section, the template generation section andthe interferometer are commonly used for said some of the optical pulsesignals which have been wavelength division multiplexed.

In the fourth embodiment, the wavelength division multiplexing section45 may be structured so as to output optical pulse signals into a freespace, and such an array second spatial light phase modulation sectionas shown in FIG. 7 may be used as the second optical phase modulationsection 46. This makes it possible to use the ultra widebandcommunication system for optical space transmission of wavelengthdivision multiplexed signals.

While the present invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

INDUSTRIAL APPLICABILITY

An ultra wideband communication device according to the presentinvention is useful, for example, to construct a backbone for shortpulse radio UWB (Ultra Wide Band) signals. Also, the ultra widebandcommunication device can be used as, e.g., an optical transmissiondevice for multiplexing a short pulse signal on a CATV signal andtransmitting a resultant signal, or as an optical space transmissiondevice using a free space.

1. An ultra wideband communication system for converting a pulse signalinto an optical pulse signal, transmitting the optical pulse signal, anddemodulating the transmitted optical pulse signal, the systemcomprising: at least one pulse generation section for generating thepulse signal based on a data signal; at least one first optical phasemodulation section for performing optical phase modulation in accordancewith the pulse signal generated by the pulse generation section, andoutputting a resultant signal as the optical pulse signal; an opticaltransmission path for propagating the optical pulse signal outputtedfrom the first optical phase modulation section; a template generationsection for generating a pulse which has a correlation with the pulsesignal and which has a predetermined waveform, and outputting the pulseas a template signal; a second optical phase modulation section for, inaccordance with the template signal outputted from the templategeneration section, performing optical phase modulation on the opticalpulse signal propagated through the optical transmission path, andoutputting a resultant signal as an optical phase demodulation signal;an optical phase intensity conversion section for converting informationabout an optical phase of the optical phase demodulation signaloutputted from the second optical phase modulation section intoinformation about an optical intensity thereof, and outputting aresultant signal as an optical correlation signal; at least oneoptical-electrical conversion section for performing optical-electricalconversion on the optical correlation signal outputted from the opticalphase intensity conversion section, and outputting a resultant signal asa correlation signal; and at least one signal identification section fordetecting the data signal by identifying the correlation signaloutputted from the optical-electrical conversion section.
 2. The ultrawideband communication system according to claim 1, wherein more thantwo: pulse generation sections; first optical phase modulation sections;optical-electrical conversion sections; and signal identificationsections are provided, the ultra wideband communication system furthercomprising: a wavelength division multiplexing section for performingwavelength division multiplexing of optical pulse signals respectivelyoutputted from the first optical phase modulation sections, and thenpropagating the optical pulse signals through the optical transmissionpath; and a wavelength demultiplexing section provided on an output sideof the optical phase intensity conversion section, wherein the secondoptical phase modulation section performs, in accordance with thetemplate signal outputted from the template generation section, opticalphase modulation on a plurality of optical pulse signals multiplexed bythe wavelength division multiplexing section, and outputs resultantsignals as optical phase demodulation signals, the wavelengthdemultiplexing section wavelength demultiplexes the optical correlationsignals, which have been outputted from the optical phase intensityconversion section, in accordance with wavelengths of the signals, andoutputs resultant signals as optical correlation signals, theoptical-electrical conversion sections perform optical-electricalconversion respectively on the optical correlation signals outputtedfrom the wavelength demultiplexing section, and respectively outputresultant signals as correlation signals, and each of the signalidentification sections identifies one of the correlation signalsoutputted from a corresponding one of the optical-electrical conversionsections, thereby detecting a data signal.
 3. The ultra widebandcommunication system according to claim 2, wherein an interval betweenwavelengths of the plurality of optical pulse signals is an integralmultiple of a free spectrum range of the optical phase intensityconversion section.
 4. The ultra wideband communication system accordingto claim 1, wherein the first optical phase modulation section performsoptical phase modulation by an external modulation method.
 5. The ultrawideband communication system according to claim 1, wherein the firstoptical phase modulation section performs optical phase modulation by adirect modulation method.
 6. The ultra wideband communication systemaccording to claim 1, wherein the optical phase intensity conversionsection is structured by an interferometer.
 7. The ultra widebandcommunication system according to claim 6, wherein the optical phaseintensity conversion section uses transfer factor characteristics, whichare different from each other in relation to an optical phase of theoptical phase demodulation signal, so as to output two opticalcorrelation signals respectively having optical intensities which areopposite to each other with respect to a reference optical intensity,and the optical-electrical conversion section is structured by a bipolarphotodiode to which the two optical correlation signals are inputted. 8.The ultra wideband communication system according to claim 1, whereinthe optical phase intensity conversion section is structured by anoptical filter.
 9. The ultra wideband communication system according toclaim 1 wherein the optical phase intensity conversion section isstructured by an adaptive photodetector.
 10. The ultra widebandcommunication system according to claim 1, wherein the second opticalphase modulation section is structured by a spatial light phasemodulator, and the optical transmission path is a free space.
 11. Theultra wideband communication system according to claim 1, wherein thefirst optical phase modulation section performs, in accordance with thepulse signal, phase modulation in either one of two manners, in one ofwhich the first optical phase modulation section performs phasemodulation such that an optical phase changes in a direction from 0 toπ, and in another of which the first optical phase modulation sectionperforms phase modulation such that an optical phase changes in adirection from πto 0, and the second optical phase modulation sectionperforms, in accordance with the template signal which is uniquely set,phase modulation in a predetermined manner regardless of the datasignal, the predetermined manner being either one of two manners, in oneof which the second optical phase modulation section performs phasemodulation such that an optical phase changes in a direction from 0 toπ, and in another of which the second optical phase modulation sectionperforms phase modulation such that an optical phase changes in adirection from πto
 0. 12. An optical transmission device used in anultra wideband communication system for converting a pulse signal intoan optical pulse signal, transmitting the optical pulse signal, anddemodulating the transmitted optical pulse signal, the devicecomprising: a pulse generation section for generating the pulse signalbased on a data signal; and an optical phase modulation section for, inaccordance with the pulse signal generated by the pulse generationsection, performing optical phase modulation, and outputting a resultantsignal as an optical pulse signal, wherein the optical phase modulationsection performs phase modulation in either one of two manners, in oneof which the optical phase modulation section performs phase modulationso as to cause an optical phase to change in a direction from 0 to π,and in another of which the optical phase modulation section performsphase modulation so as to cause an optical phase to change in adirection from π to 0, such that: after the optical pulse signal ispropagated through the optical transmission path, optical phasemodulation is performed on the optical pulse signal in accordance with apredetermined template signal having a correlation with the pulsesignal, in order for the optical pulse signal to be converted into anoptical phase demodulation signal; information about an optical phase ofthe optical phase demodulation signal is converted into informationabout an optical intensity thereof, in order for the optical phasedemodulation signal to be converted into an optical correlation signal;and optical-electrical conversion is performed on the opticalcorrelation signal in order for the optical correlation signal to beconverted into a correlation signal.
 13. An optical reception deviceused in an ultra wideband communication system for converting a pulsesignal into an optical pulse signal, transmitting the optical pulsesignal, and demodulating the transmitted optical pulse signal, thedevice comprising: a template generation section for generating a pulsewhich has a correlation with the pulse signal and which has apredetermined waveform, and outputting the pulse as a template signal;an optical phase modulation section for, in accordance with the templatesignal outputted from the template generation section, performingoptical phase modulation on the optical pulse signal, on which opticalphase modulation has been performed such that an optical phase of theoptical pulse signal changes in a direction from 0 to π, or in adirection from π to 0, and for outputting a resultant signal as anoptical phase demodulation signal; an optical phase intensity conversionsection for converting information about an optical phase of the opticalphase demodulation signal outputted from the optical phase modulationsection into information about an optical intensity thereof, andoutputting a resultant signal as an optical correlation signal; anoptical-electrical conversion section for performing optical-electricalconversion on the optical correlation signal outputted from the opticalphase intensity conversion section, and outputting a resultant signal asa correlation signal; and a signal identification section for detectinga data signal by identifying the correlation signal outputted from theoptical-electrical conversion section.
 14. An optical repeater used inan ultra wideband communication system for performing wavelengthdivision multiplexing of a plurality of optical pulse signals, on eachof which optical phase modulation has been performed in accordance witha plurality of pulse signals, transmitting the plurality of opticalpulse signals, and wavelength demultiplexing the plurality oftransmitted optical pulse signals to demodulate the optical pulsesignals, wherein the optical pulse signals are signals, on each of whichoptical phase modulation has been performed such that an optical phaseof each of the optical pulse signals changes in a direction from 0 to π,or in a direction from π to 0, the optical repeater comprising: atemplate generation section for generating a pulse which has acorrelation with each of the pulse signals and which has a predeterminedwaveform, and outputting the pulse as a template signal; an opticalphase modulation section for, in accordance with the template signaloutputted from the template generation section, performing optical phasemodulation on the plurality of optical pulse signals which have beenwavelength division multiplexed, and outputting resultant signals asoptical phase demodulation signals which have been wavelength divisionmultiplexed; and an optical phase intensity conversion section forconverting information about an optical phase of each of the opticalphase demodulation signals, which have been wavelength divisionmultiplexed and which have been outputted from the optical phasemodulation section, into information about an optical intensity thereof,and outputting resultant signals as optical correlation signals havingbeen wavelength division multiplexed.